Non-magnetic medical infusion device

ABSTRACT

Liquid infusion apparatus includes non-magnetic materials in a pumping structure and drive motor therefor, and in a controller that supplies drive signals to the motor to facilitate convenient operation in intense magnetic fields without distorting the magnetic fields and without radiating objectionable radio-frequency interface.

FIELD OF THE INVENTION

This invention relates to the field of liquid infusion apparatus andmore specifically to such apparatus for operation during study within aMagnetic Resonance Imaging (MRI) system in which extraneous radiofrequency (RF) signals and magnetic materials within the MRI'senvironment cause detrimental interference to the imaging process, upsetthe function of the infusion device, and present hazards to the patient.

BACKGROUND OF THE INVENTION

It is desirable to carefully control the intravenous (IV) administrationof liquids to a patient. Conventional gravity IV solution delivery viacommonly-available IV administration sets is typically not sufficientlyaccurate for the delivery of many types of fluids and drugs. Variouspositive displacement pumping devices have been developed for carefullycontrolling such IV administration. Some types of IV pumps control flowwithin a standard IV administration set via peristaltic (either linearor rotary) pumping schemes directly on the tubing of a conventional IVinfusion set, other types may incorporate a proprietary volumetriccassette, still others utilize a syringe-like device. However, therecurrently exists no IV controller(s) capable of completely safeoperation within a MRI suite wherein a considerable need exists for thecontrolled delivery of medicinal liquids. Frequently, patients scheduledfor MRI examination arrive at the MRI suite with IV solutions beingadministered and controlled by devices which must be disconnected as thepatient is moved into the suite where high magnetic fields are presentand no outside RF interference can be tolerated.

The basic characteristics of an infusion pump involve the delivery ofmedicinal or nutritional liquids, over time, into the venous system of aliving subject. Certain physical limitations regarding the delivery rateand pressure are elemental in IV liquid-infusion control. IV fluids arepumped at pressures typically in the range of 0.2 to 10 PSI. Theinfusion device should include detection of over-pressure andoperational limits at not more than about 20 PSI. Flow ranges typical ofIV pumps are from 0.1 to 2000 ml/hr. Such specifications forconventional IV infusion apparatus are quite different from thespecifications for Injector devices which are often used in radiologicsettings, including MRI, for purposes of very rapid bolus injection ofimage enhancing contrast agents. Such devices ‘push’ contrast agents atpressures up to 300 PSI and in very short periods of time in contrast toIV drug delivery. Contrast agents are solely for image enhancement andhave no medicinal value in a patient.

The high magnetic field surrounding MRI systems can negatively affectthe operation of various devices (including conventional IV controldevices), especially those devices that are constructed with magneticmaterials, and can seriously jeopardize a patient's safety as a resultof devices utilizing magnetic materials that can be attracted at highvelocity into the magnetic field of the MRI system where patient orattendant personnel are located.

Conventional devices for infusing liquids into a patient are typicallysmall portable units often attached to an IV pole holding both theinfusion device and associated liquids to be infused. Some of suchdevices utilize either stepper-type motors or simple DC motors whichinclude magnetic materials for providing the mechanical power requiredto drive the pumping unit. Further, some form of electronic control unitreceives the user's prescribed infusion rate settings and controls thepumping unit to deliver the desired quantity of liquid over time, andsuch control unit may emit spurious radio frequency signals as a resultof poor electrical design or insufficient shielding.

With the advent of MRI procedures for the imaging of internal bodystructures, very special requirements must be satisfied in the design ofmedical devices intended to be used within the MRI environment. MRIsystems exploit the physical phenomenon of nuclear magnetic resonance(NMR) by which RF stimulation of atomic nuclei within an associatedmagnetic field results in the emission of a small RF ‘spin echo’ fromthe nucleus so stimulated. In the case of patient imaging, hydrogennuclei bound with water are the usual targets for magnetic resonance atselected frequencies. Other molecules and compounds can also be selectedfor study, as in Nuclear Magnetic Spectroscopy, by choosing resonancespecific magnetic field strengths and associated radio frequencies. Forsimplicity the typical hydrogen atom-based MRI image-acquisition processis referred to herein, but it should be recognized that the subjectinvention is equally useful in MRI spectrographic studies at a pluralityof field strengths and frequencies.

The typical MRI system includes several components, as shown in FIG. 1.For example, the operator's console 25, 27 and various processing 37,display 29, 31 and radio frequency and magnetic gradient amplifyingequipment 33, 35 are all located outside of the environment of the MRIscanning suite which must be configured to eliminate image-degradingradio frequency interference and field effects of metallic structuresthat can introduce field distortions and become safety hazards. The MRIscanning unit produces large magnetic and RF fields, and must be capableof receiving the extremely small RF nuclear ‘echoes’, and is thereforetypically located within a shielded room 11. Such rooms greatlyattenuate outside RF noise and may also some provide containment of thescanner's magnetic field.

However, certain devices are required to be placed in the scan roomeither to assist with care of the patient being imaged or for the use ofattending staff. Of particular interest are those devices which must beplaced in the scan room during the time of image acquisition when thepatient is present and the magnetic fields are ‘up’ and RF reception ofthe tiny. nuclear ‘echoes’ must be cleanly acquired. Electricallypassive metallic items such as oxygen bottles or ‘crash carts’ presentsafety hazards to the patient due to their potential to be stronglyattracted by the scanner's magnetic field. Such items can be ‘pulled’into the imaging volume where the patient is located, creating potentialfor serious injury or death. Additionally, great effort is made duringthe manufacture and installation of the scanner/magnet to assure thatthe lines of flux within the imaging volume are highly homogenous toassure that acquired images have minimal spatial distortion. Thus,devices formed of magnetic material that are positioned within thescanner's magnetic field can introduce distortions into this homogeneousfield and the resultant images. The level of hazard and the degree offield/image distortion due to magnetic materials depends upon thecomposition and location with respect to the imaging volume.

The hazards due to ‘flying’ objects can be controlled to some degree bythe use of non-ferrous devices such the aluminum oxygen bottle.Additionally, the gravitational weight of some devices or their rigidfixation in the scanning room maybe sufficient to overcome the force ofmagnetic attraction on the ferrous mass of such devices toward theimaging volume. However, such devices with some ferrous mass, thoughinhibited from being pulled into the magnetic field, may neverthelessintroduce in homogeneity in the magnetic field. Distortions in thehomogeneity of the magnetic field within the imaging volume must be keptat such a level as to be of minimal consequence to the operator readingthe resultant image or data. And, the possibility of field distortion isproportionally increased as devices with metallic materials arepositioned closer to the imaging volume, with the most critical positionbeing near the center of the imaging volume, essentially where thepatient is positioned. Additionally, because of the extremely low levelsof RF signals produced by the target image nuclei, great care must betaken to assure that devices with active electronic circuits do not emitspurious RF signals as forms of electronic noise. Such noise can sodegrade the signal-to-noise ratio of signals received by the MRI sensorcoils and receivers that image resolution is reduced or renderedcompletely unreadable. Active circuits must be carefully shielded toassure that their RF emissions are extremely low at the specificfrequencies of the imaging process. Conversely, it is possible throughcareful design, to place a source of RF energy for signal transmission,therapy, or the like, within the MRI environment, but such signals mustbe chosen to avoid the discreet Lamar frequencies unique to theparticular magnetic field strength of a given MRI scanner, and must beof such high spectral purity as to coexist with the MRI without causingany deleterious effects. The intense magnetic fields produced by the MRIscanner can cause detrimental effects on the performance of common DCand stepper motors in devices needed within the MRI scanning room, tothe point of making their control difficult or causing their completefailure.

For example, injectors of image-enhancing contrast agents are commonlyrequired to inject such contrast agent during actual imagingacquisition, and such devices include motors that contain magneticmaterial and that must therefore be located at a sufficient distance toreduce interactive effects with the magnet of the MRI scanner for properoperation and safety. Controllers and consoles of electronics anddisplays that generate spurious RF signals are therefore located outsidethe MRI scan room to avoid interference with the sensitive RF receiversof the RF scanner.

Accordingly, it is desirable to provide a self-contained, MRI-compatibleinfusion pump for the relatively long term control and delivery of thevarious infusion solutions and drugs routinely delivered to a patientwithin the MRI environment during image acquisition. Such devices mustnot emit any significant RF emissions that might adversely affect imageacquisition operation from within the MRI scan room and must notinteract with the magnetic fields therein either to cause distortion ofthe field or to be influenced by these fields sufficiently to jeopardizereliable operation of such devices.

SUMMARY OF THE INVENTION

In accordance with the illustrated embodiment of the present invention asafe and effective infusion device for use within the MRI scan roomachieves reduction of magnetic material and accurate pumping control aswell as reduction of RF emissions. In one embodiment, the infusiondevice includes an ultrasonic motor that eliminates magnetic materialsand that does not produce any detrimental magnetic fields and that isnot affected by external magnetic fields. The ultrasonic motor drives aperistaltic or other suitable fluid pumping mechanism, and is driven bya multiphasic electronic signal specifically designed to produce verylittle RF harmonic noise in the spectral range of about 6 Mhz to 130 Mhzin which MRI receivers are most sensitive.

Control electronics receive commands through an input keypad for settingprescribed fluid dose to be delivered and such inputs are translatedinto signals to control the motor and pumping mechanism. Various safetydevices feed back operational information to the control electronics,including detection of motor speed and motion of pump elements, airbubbles in the fluid path, drip rate, high pressure, low fluid, low/noflow, overtime, and the like. The present infusion device includesbattery power for portability, and is housed in one RF shielded housingfor convenient location anywhere within the MRI scan room withoutintroducing image degrading RF interference or producing distortions ofthe homogeneous magnetic field, and without being affected by the strongmagnetic fields or high-level RF energy produced by the MRI system. Suchunrestricted placement of the device is of great importance to thesafety and convenience of the attending MRI staff and imaging patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial plan view of a conventional MRI system showingtypical placement of operational components;

FIG. 2 is a partial perspective view of an infusion device in accordancewith one embodiment of the present invention; and

FIG. 3 is a block schematic diagram of the infusion device of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the plan view in FIG. 1 of an MRI system, the scanningroom 9 is disposed within shielding boundary walls 11, with a controlroom 13 for operators or attendant personnel positioned outside theboundaries of the scanning room 9. The scanning room 9 includes theimage acquisition equipment including a source 15 of intense magneticfield 16 that emanates from the source in substantially homogenous arraythroughout the adjacent space and around a patient 17. Variouscomponents of the system for performing the image acquisitionoperations, including gradient 19 and sensor 21 and RF coils 23 aredisposed about the patient 17 for stimulating the nuclei ‘echos’ to mapthe positions thereof within the spatially-homogenous magnetic field 16as the patient's body is scanned in conventional manner along multipleorthogonal axes. The shielding boundary walls 11 (and ceiling and floor)provide shielding against radio-frequency interference and, asfabricated with ferrous materials, may also establish outer limits ofthe magnetic field distribution around magnetic 15.

The control room 13 is disposed outside the shielding boundary walls 11and is equipped with computer input keyboard 25, computer display 27,monitor 29 of patient's vital life signs, controls 31 for liquidinfusion apparatus, and the like. Such representative equipment ishoused outside the shielding boundary walls 11 to inhibit intrusion ofspurious magnetic and electrostatic and RF signals into the imageacquisition operations within the scanning room 9. Similarly, thegradient amplifiers 33 for amplifying signals from conventional gradientcoils 1921, along X, Y, and Z coordinates and RF amplifiers 35 and theimage-processing computer 37 are also located outside the shieldingboundary walls 11 for the same reason. The thru-wall interconnections 39between the components within the scanning room 9 and the electronicequipment 25, 27, 29, 31, 33, 35, 37 disposed outside the room 9typically also includes RF shielding to diminish the sources and theportals by which and through which RFI signals may enter the scanningroom 9.

A liquid-infusion device 41 commonly resides within the scanning room 9to administer IV injection into the patient 17 of liquid compositions,for example, that enhance image acquisition (e.g., contrast medium) orthat otherwise provide diagnostic or therapeutic benefits to the patient17 being scanned. Such conventional infusion device 41 should desirablybe positioned close to the patient 17 to facilitate IV liquid infusion,but must be positioned remotely to avoid disrupting the homogeneousmagnetic field 16, and to minimize RFI and operational failures of theinfusion device 41 resulting from operating in the intense magneticfield adjacent the patient 17. Control of such infusion device 41 may bevia remote controller 31 disposed within control room 13.

In accordance with the embodiment of the invention illustrated in FIG.2, an improved liquid infusion device 43 is operable within intensemagnetic fields and with negligible RFI to provide positive displacementof a liquid 45 such as saline or contrast medium, or sedative, or thelike, in controlled volumes per unit time. The device does not includeany ferrous or magnetic materials, and is substantially shielded againstirradiating any RFI during operation. Specifically, the device 43includes a pump in the lower chamber 47, as later described herein. Thepump chamber 47 receives therein the flexible, resilient tubing 49 thatis pre-packaged and sterilized as a component of a conventional IVliquid infusion set that also includes a conventional drip chamber 51 aspart of the infusion set. Controls for the pump in chamber 47 include anoperator's input keypad 48 for setting infusion parameters, and a dripdetector 85 that can be disposed about the drip chamber 51 to detectflow of liquid from the supply 45. A display 53 is positioned in theupper portion of the housing 55 which may be formed of non-magnetic,RF-shielding material such as conductively-coated plastic or aluminum,or the like. The housing 55 attaches with one or more clamps 57 to arigid support 59 formed of non-magnetic material such as fiberglass oraluminum, or the like. Various visual and audible annunciators 61 may beprovided to signal operational conditions either within acceptablelimits, or within error or failure conditions.

Referring now to the pictorial block schematic diagram of FIG. 3, thereis shown a peristaltic-type positive-displacement pump 60 disposedwithin the pump chamber 47 of the housing 55 to operate with the lengthof tubing 49 that passes therethrough between the drip chamber 51 andthe patient. The peristaltic pump 60 (linear or rotational) is driven byan ultrasonic motor 64 via appropriate mechanical linkage 65 to actuatea squeeze roller against the tubing 49 in known peristaltic pumpingmanner, or to actuate a series of elements 67 through a lineartubing-squeezing sequence to produce peristaltic pumping action in knownmanner.

A conventional ultrasonic driving motor 64 is powered in known manner bymultiphasic signals applied thereto from the motor drive circuit 69. Acontroller 71 for the device includes a central processing unit 73 withassociated peripheral components including Random Access Memory 75,Read-Only Memory 77, Digital-to-Analog converter 79, and an Input/Outputchannel 81. This controller 71 receives input control information fromthe operator's keypad 48, and receives feedback information about motionof pump elements from sensor 84, about pump speed from sensor 83 andabout liquid flow from drip detector 85 disposed about the drip chamber51. In response to the inputs supplied thereto, the controller 71operates on stored programs to actuate a display 53 of operatingparameters (or other data), and to actuate the motor drive circuit 69for energizing the ultrasonic motor 64 for rotation at a controlledspeed. A power supply 63 is connected to the controller 71 and drivecircuit 69 to supply electrical power thereto, and is connected to abattery 87 to receive electrical power therefrom during stand-aloneoperation, or to receive line voltage via plug 63, as required.

In accordance with this embodiment of the present invention, no magneticmaterial is used in any of the components of the infusion device 43including the ultrasonic motor 64, pump 60, power supply 63, controller71 and associated components. Additionally, none of such components isadversely affected during operation by a strong magnetic field. And, anyRF energy that may be generated by electronic signals within theultrasonic motor 64, drive circuit 69, controller 71, power supply 63 orassociated components is specifically shielded by conductive structures91, 93 disposed around such components to inhibit radiation of RFI.Additionally, radio-frequency interference filters 95 are disposed aboutall throughshield conductors to inhibit radiation of RFI through suchportals.

Therefore, the liquid infusion device of the present invention isconfigured without magnetic materials for operation within intensemagnetic fields to administer I.V. fusion of liquids to a patient in anMRI environment. The infusion device may be positioned close to apatient during image acquisition without significantly distorting thehomogeneous magnetic field around an MRI scanner, and without emittingharmful RFI in the vicinity around a patient from whom extremelylow-level RF ‘echos’ are being detected during image acquisition.

1. An IV infusion delivery apparatus for operation in an MRIenvironment, the apparatus comprising: a linear peristaltic pumpconstructed of non-magnetic material disposed to receive a liquidconduit linearly oriented therein and to transfer liquid through theliquid conduit from a liquid IV container source in response tomechanical motion of a plurality of pump elements; an ultrasonicactuator constructed of non-magnetic material disposed within anelectrically conductive structure and coupled to provide mechanicalmovement to the pump in response to applied multiphasic electricalsignals to provide positive displacement of the IV liquid from the IVcontainer source; a sensor that detects the mechanical motion of atleast one of the plurality of pump elements to produce an output signalindicative thereof; a sensor disposed to produce an output signalindicative of liquid flow pumped through the pumping structure; and acontroller including a central processing unit and memory that storesoperating programs disposed within an electrically conductive structureand constructed of non-magnetic material for operation in an MRIenvironment, the controller communicating with the sensors to receivethe output signals therefrom, and with the ultrasonic actuator toselectively energize the actuator to drive the pump, and therebytransfer liquid from the IV container source through the liquid conduitat a controllable volumetric rate.
 2. The IV infusion delivery apparatusof claim 1, further comprising a sensor disposed to produce an outputsignal indicative of speed of the ultrasonic actuator.
 3. The IVinfusion delivery apparatus of claim 1, wherein the sensor that detectsmechanical motion also provides an output indicative of speed of theultrasonic actuator.
 4. An IV infusion delivery apparatus for operationin an MRI environment, comprising: a non-magnetic, linear peristalticpump disposed to receive a liquid conduit therein, said pump having aplurality of pumping elements; a non-magnetic, ultrasonic actuatordisposed within a conductive structure that operates the pump to providepositive displacement of IV liquid from an IV container source inresponse to applied multiphasic signals at ultrasonic frequencies; asensor that detects motion of the pumping elements and produces anoutput signal indicative thereof; a sensor that detects liquid flowpumped through the liquid conduit and produces an output signalindicative thereof; and a controller including a processor and memoryoperable in an MRI environment and disposed within a conductivestructure, the controller applying the multiphasic signals at ultrasonicfrequencies to the ultrasonic actuator to operate the pump in responseto the outputs from the sensors, to move liquid from the IV containersource through the liquid conduit.
 5. An IV infusion delivery apparatusfor operation in an MRI environment, the apparatus comprising: a linearperistaltic pump constructed of non-magnetic material disposed toreceive a liquid conduit linearly oriented therein and to transferliquid through the liquid conduit from a liquid IV container source inresponse to mechanical motion of a plurality of pump elements; anultrasonic actuator constructed of non-magnetic material disposed withinan electrically conductive structure and coupled to provide mechanicalmovement to the pump in response to applied multiphasic electricalsignals to provide positive displacement of the IV liquid from the IVcontainer source; a sensor that detects the mechanical motion of atleast one of the plurality of pump elements to produce an output signalindicative thereof; and a controller including a central processing unitand memory that stores operating programs disposed within anelectrically conductive structure and constructed of non-magneticmaterial for operation in an MRI environment, the controllercommunicating with the sensor to receive the output signal therefrom,and with the ultrasonic actuator to selectively energize the actuator todrive the pump, and thereby transfer liquid from the IV container sourcethrough the liquid conduit at a controllable volumetric rate.